C12E7-DPPC mixed systems studied by pyrene fluorescence emission

Abstract

The lipid/surfactant mixed interactions between the lipids dipalmitoylphosphatidylcholine (DPPC) or egg phosphatidylcholine (EggPC) and the non-ionic surfactant C12E7 [C12H 25(OCH2CH2)7OH] were studied by the use of the fluorescence properties of pyrene, namely the excimer to monomer emission intensity ratio, IE/IM. Previously, the behaviour of the C12E7/water system was also monitored. It was found to exhibit a significant preassociation of pyrene in ground state, which is more pronounced in micelles than in premicellar aggregates. In mixed systems, pyrene has proved to detect the changes from mixed bilayers to mixed micelles. The temperature influence in lipid/surfactant interactions was also studied. It was found that the pyrene IE/IM ratio is sensitive to the phase transition of DPPC. Pyrene microcrystallites are probably present in the gel phase region, justifying the enhancement of IE/IM in the DPPC/C12E7 system at low temperatures.